Simulation And Prediction Of The Impact Of Climate Change On Net CO₂ Exchange In Alpine Meadow Of Northern Tibet

Ecosystem carbon cycle is strongly affected by the climate change,and plays an important regulatory role in global climate change.Alpine meadow is the most important ecosystem in the Qinghai Tibet Plateau and is very sensitive to climate change.Alpine meadow has high soil carbon storage,strong carbon sink potential,and significant contribution to the CO₂ exchange between vegetation and atmospheric interface.However,the model simulation of net CO₂ exchange?NEE?response to climate change is still lacking.Therefore,in order to scientifically evaluate the contribution of Alpine meadow sources and sinks and reveal the different response of nee to climate change in growing and non growing season,based on the Daycent model,this study simulated and analyzed the change of NEE in Alpine meadow in Northern Tibet from 1971 to 2017,explored the response and adaptation process of NEE to climate change,and simulated the different future?2020-2099?under the climate change scenario,the dynamic trend of carbon budget pattern in Alpine meadow.The main conclusions are as follows:?1?Daycent model is suitable for simulating the dynamic change of NEE in Alpine meadow.The validation of Daycent model by NEE flux data of Alpine meadow from 2012 to 2017 at Nagqu station in Northern Tibet show that the simulated value and the measured value keep a high consistency,R² value is between 0.62 and 0.91,RMSE value range is 0.32 to 0.74 gC·m^-2;Comparing the simulation results in different season,it is found that the simulation effect of NEE in growing season?R²=0.35?is better than that in non growing season?R²=0.12?.?2?From 1971 to 2017,the temperature of Nagqu in Northern Tibet showed a significant upward trend?p<0.05?.The annual average temperature increases by 0.5°C?R²=0.69?every ten years,and the non growing season is more intense than the growing season.The average temperature increases by0.6°C/10a?R²=0.58?and 0.4°C/10a?R²=0.62?respectively.The annual precipitation is 446.6 mm,and89%of the precipitation is concentrated in the growing season.The interannual and seasonal fluctuation of precipitation is large,and there is no significant change trend.The Alpine meadow in Northern Tibet showed weak carbon sink.The annual NEE is 2.7±2.8 gC·m^-2,in which the growing season is the net absorption of CO₂,119.2 gC·m^-2,and the non growing season is the net emission of CO₂,116.5 gC·m^-2.The annual and seasonal fluctuation of nee is large,and there is no significant change trend.?3?In the future,the climate in Northern Tibet will be warm and humid.Based on the measured climate data from 1971 to 2017,the temperature and precipitation in 2020-2099 under the scenarios of RCP4.5 and RCP8.5 increased significantly?p<0.05?.In the RCP8.5 scenario,the annual average temperature increased significantly to 2.2°C compared with the reference period?-0.6°C?,the annual precipitation increased from 446.6 mm to 598.5 mm in the same period,the average temperature rise rate?0.8°C/10a?in the non growing season was faster than that in the growing season?0.7°C/10a?,and the precipitation growing rate?24.6 mm/10a?in the growing season was greater than that in the non growing season?5.1 mm/10a?.In the future,the Alpine meadow in Northern Tibet shows the function of carbon sink.Compared with the reference period NEE,under the RCP8.5 scenario,the annual NEE was significantly increased to 10.6 gC·m^-2,while in the growing season NEE was significantly increased to129.0 gC·m^-2?p<0.05?,while in the non growing season NEE had no significant change?p>0.05?.When NEE increased significantly in the growing season and decreased significantly in the non growing season p<0.05),the annual fluctuation of NEE was large and there was no significant change trend.Therefore,in the future warm and humid scenario,the carbon sink of Alpine meadow ecosystem will increase,and the carbon sequestration capacity will increase mainly in the growing season.To sum up,under the current climate warming situation in Northern Tibet,Alpine meadow presents carbon sink,and under the trend of future climate warming and humidification,the carbon sink function of Alpine meadow will be enhanced.The response of NEE to climate change in Alpine meadow in Northern Tibet is seasonal.Although the increase of temperature in non growing season is significantly higher than that in growing season,there is no significant change of NEE in non growing season under the future climate change scenario.However,the temperature in growing season is relatively high with abundant precipitation,and the trend of warm and humid makes the carbon sink function of Alpine meadow significantly strengthened.It can be seen that the Alpine meadow has strong adaptability,can make full use of the favorable water and heat conditions in the growing season under the warm and wet climate scenario,and promote the increase of carbon absorption.